Insert fails ORA-24345

Hi,
We've got a PC controlled machine at a client's site. When the machine
finishes a batch process a text file of the results is generated. A
utility I've written uses SQL*Loader to squirt this data into and
Oracle table. The utility then performs some analysis on this data and
puts the results in an "export" table. This export table is a mirror
of a table on the clients network. The utility checks that a database
link is open, then inserts the data into the remote table. At least
its meant to.

When our clients signed off the final tests the remote table was
simulated on their laptop. Everything worked fine. Now its come to
their site and the final INSERT to the remote table fails with error
messages:

A select can be executed against the remote table without a problem.
(DESC fails but I think that's another issue). Using 8.1.7.0.0 on our
PC, not sure what version's at the other end but inserting data over
other dblinks from other PCs works ok.